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Human Image Formation

Human Image Formation. What is the quality of the optics of the human eye? How can we measure it and describe it empirically?. 17 mm. The Cornea and Lens Focus the Image on The Retina. Cross-Section of a Real Eye. Lens. Retina. Cornea. Optic disk. Iris. Optic nerve.

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Human Image Formation

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  1. Human Image Formation • What is the quality of the optics of the human eye? • How can we measure it and describe it empirically?

  2. 17 mm The Cornea and Lens Focus the Image on The Retina

  3. Cross-Section of a Real Eye Lens Retina Cornea Optic disk Iris Optic nerve

  4. Chemical accident at 3 yrs • One eye lost; other cornea destroyed • Blind from age 3 through 46 • Stem cell replacement in right eye for both epithelium and stem cells Corneal epithelium cells Limbic stem cells Recovered Sight(Fine, Wade, Wandell) Primary visual cortex is one-fourth the normal size Motion selective cortex is the normal size

  5. Structure of the lens Special cellular properties that permit the lens to stretch The fibrous nature of the lens is evident in low-magnification scanning Lens fibers (micrograph 2) are mature cells that have lost their organelles, including nuclei, and are packed with soluble structural proteins called crystallins. The age-related decrease in the ability of the lens to accommodate for near vision is, in part, related to the accumulation of more lens fibers, but it is due primarily to decreased elasticity of the capsule.

  6. Socket and knob interdigitations maintain lens organization Mature lens fibers are tightly packed and join with one another via knob- and socketlike associations (k, micrograph 2). These elaborate cell interdigitations maintain the lens organization during shape changes associated with accommodation. In addition, close packing of cells prevents excess light scattering and facilitates communication between adjacent cells.

  7. Things I don’t know and would like to • What governs the development of optical power of the eye? (Wiesel recent work) • What are the material properties of the cornea and lens that give them their refractive power? • What happens to these materials when cataracts develop?

  8. GCL INL ONL OS Light enters Inner Outer Light Passes Through The Retinal Cells And Is Absorbed by the Rods and Cones

  9. Light Scattered From From The Retina Is Used To Estimate Optical Quality(e.g., Campbell and Gubisch)

  10. Measurements Of Light Reflected From The Retina (Linespread) At Various Pupil Diameters

  11. The Linespread Function Is A Useful Summary of Optical Quality Analyzing slit position

  12. Simple Lenses and Many Other Optical Systems Satisfy the Linear System Priniciple of Homogeneity

  13. Superpositionand Shift-invariance Are Different Properties Of A Linear System: Linear Systems Are Not Always Shift-Invariant

  14. Harmonic patterns are widely used in vision science research M = mean level, a = contrast, f = spatial frequency

  15. Harmonics have a special role in shift-invariant linear systems because they pass through only slightly altered

  16. + … + … + … Every image can be described as the weighted sum of harmonics F = 1 F = 6 F = 9

  17. Approximation by harmonics improves as we add more harmonics together Sum of the first N harmonics 3 6 12 24 48 64

  18. We can use shift-invariance and harmonics to correct for the double pass experiment What they measured What they want to know

  19. Campbell and Gubisch: analysis 1.5mm 2.0 mm 2.4 mm 3.0 mm 6.0 mm 4.9 mm 3.8 mm 5.8 mm Diffraction limit

  20. Inferred linespread (Westheimer)

  21. We can describe a system’s performance with respect to its treatment of harmonics:The Modulation Transfer Function (MTF) Reduction of the harmonic amplitude

  22. 1 0.75 Relative amplitude 0.5 Ijspeert 0.25 Westheimer 0 10 20 30 40 50 Frequency (cpd) Theoretical MTFs are similar to the data, but not exact: This is a 10% Field

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